Why do I have to give my pet heartworm prevention year round?

Heartworm prevention is recommend year round to give your pet his best chance of staying heartworm free. No one knows when the first mosquito will come out, or when the last will die. Furthermore, it is possible for mosquitoes to live indoors, even in the winter! If you stop giving your pet prevention, then start back up again, and they have contracted heartworms, it puts your pet in great danger and could have fatal results.